One of the most powerful techniques for reproducing nanostructures—i.e. structures in the order of 100 nm or smaller—is nanoimprint lithography (NIL). In nanoimprint lithography an inverted copy of the surface pattern of a template—often called a stamp—is transferred into an object, comprising a substrate and, applied thereto, a film of a moldable layer often called resist, e.g. a polymer material. After heating the object to a temperature above the glass transition temperature of the polymer film, the stamp is pressed towards the film, cooled and released from the stamp—often called demolding—to give a polymer film with the desired pattern. This process is defined as a “thermal imprint process”. Alternatively, a photo-resist material, i.e. a resin composition, which cures upon exposure to photon radiation, covers the substrate. This so-called “Photon-imprint process” requires that either the substrate or the stamp is transparent. In a process subsequent to the imprint, the object—comprising the substrate and the patterned polymer film—can be post-processed, e.g. by etching of the substrate within the imprinted regions to transfer the pattern to a target surface of the substrate.
A method for transferring a pattern from a template to an object in an imprint process has been suggested, which involves a two-step process, which is described in JPA no. 2008-515059, U.S. patent application Ser. No. 11/450,377, U.S. patent application Ser. No. 11/268,574 and U.S. patent application Ser. No. 11/305,157.
The template or master used in an imprint process is generally a high cost product, and wear or damages to the template should therefore be minimized. The template may be made of any material, but is often made of Si, Ni, Ti, other metals, or quartz, optionally provided with an anti-stick layer. On the other hand, the object to be imprinted is often made of a relatively hard material, such as glass, quartz, a metal, a metal-oxide, silicon, or another semiconductor material, sometimes coated with different layers comprising metal, alloys, organic or carbonaceous materials. On their surfaces a comparatively soft moldable imprint layer is exposed. The imprinting of the object is a crucial moment, where parallel arrangement is important, and a very small residual layer of the moldable layer, often in the order of less than 10 nm, under the imprinted protruding structures is desired. Any non-parallel arrangement or excessive pressure may therefore cause damage to the template. By the suggested two-step imprint method, the template will only be used against a polymer material, which is softer than the template material, thereby minimizing the risk of damage.
If the template and the substrate are not made of the same material, which they generally are not, they will typically have different thermal expansion coefficients. This means that during heating and cooling of the template and the substrate, the extent of expansion and contraction will be different. Even though the dimensional change is small, it may be devastating in an imprint process, since the features of the pattern to be transferred are in the order of micrometers or even nanometers. The result may therefore be reduced replication fidelity.
One of the most crucial properties in the photon-based 2-step imprint process is the anti-sticking or anti-adhesion properties between both interfaces of 1) the original template and the IPS resist and 2) the cured and patterned IPS resist and the substrate resist.